From: "Wolfgang Nádasi-Donner" <ed.odanow@...>
Date: 2009-03-08T22:34:14+09:00
Subject: [ruby-core:22739] Re: Ruby 1.9.1 and tail recursion optimization

Wolfgang N�dasi-Donner schrieb:
> Moin, moin!
> 
> I was a little bit surprized that the following code snippets run into 
> stack overflow...
> 
> myprompt> irb191-p0
> irb(main):001:0> def a
> irb(main):002:1>   b=2+1
> irb(main):003:1>   a
> irb(main):004:1> end
> => nil
> irb(main):005:0> a
> 
> ...and...
> 
> myprompt> irb191-p0
> irb(main):001:0> f = lambda{print "-";STDOUT.flush;f[]}
> => #<Proc:0xee2870@(irb):1 (lambda)>
> irb(main):002:0> f[]
> 
> ...because I thought Ruby 1.9.1 has tail recursion optimization 
> implemented.
> 
> Was this a wrong assumption?
I read one minute ago in German Ruby-Forum, that it isn't implemented in 
Ruby 1.9.1. One main reason was, that it is not possible under JVM.

Tail recursion optimization is an implementation detail, a very 
important one for functional programming, but not a feature of the 
language itself.

So why not ad a constant, maybe named TAILRECURSION, which will be set 
to true, if tail recursion optimization is supported as a feature of the 
implemntation?

If one wants use Ruby 1.9.n as a vihicle for functional programming this 
optimization is an important thing.

Wolfgang N�dasi-Donner